PTES was founded in 1977. Originally based in South Kensington at Imperial College London, in 1993 the organisation moved to its present location in Battersea, south-west London. In 2001 PTES developed Mammals Trust UK, a restricted fund and campaign targeting the conservation of Britishmammals. In 2006, Mammals Trust UK was incorporated under the activities of PTES. PTES still operates a ring-fenced funding stream for British mammals but the names ‘Mammals Trust UK’ and 'Mammals Trust' have since been disbanded.

PTES exists to support and restore our natural heritage – the diverseassemblages of species and their habitats present on Earth – through practical conservation and by educating and informing people about its importance. The charity supports conservation projects and research both in the UK and abroad through three funding schemes: ‘worldwide grants’, ‘UK mammals grants’ and ‘internship awards’.[2] The charities' work in the UK has a focus on mammals, with hazel dormouse, European hedgehog and European water vole current target species. Saproxylic beetles are also a target group, and traditional orchards a target habitat. Assistance from volunteers and collaboration with other environmental organisations are both integral to this work.

PTES runs several national, public-participation surveys aimed at monitoring wild populations and habitats. This includes the two mammal surveys that now have been running for over a decade: Living with Mammals (2003) and Mammals on Roads (2001). It was a founding member of the Tracking Mammals Partnership.[3]

Mammals on Roads (2001–present): an annual survey collecting records of mammal road casualties ('roadkill') on journeys along single carriageways. Changes in counts (over a given distance) from year to year are used to estimate changes in the wider population.[4]

The Traditional Orchard Survey of England and Wales: (2006 – present): orchards and fruit trees provide a highly biodiverse habitat and are listed as a Priority Habitat under the UK Biodiversity Action Plan (BAP). PTES is creating a UK inventory and map of the habitat.

The Hedgehog Hibernation Survey (2012–2014): runs between 1 February and 31 August, collecting sightings of dead and alive hedgehogs through the Hedgehog Street website.[5]

PTES maintains the National Dormouse Monitoring Programme (NDMP).[6] This is based on around 400 woodland sites where at least fifty dormouse nest boxes have been put up, per site, that are inspected by licensed volunteers at monthly intervals between May and October. In 2014, PTES collated 6,827 hazel dormice records from 387 sites.[7]

In 2015 PTES launched a new project to try and coordinate conservation efforts for the water vole - an animal that has declined by over 90% in Britain since the 1980s.[8] The National Water Vole Monitoring Programme is the first ongoing monitoring scheme for this species in the UK and aims to bring together data from several hundred sites to allow the status of the species to be assessed year-on-year.[9]

Linking gardens is central to Hedgehog Street as impermeable garden fences and walls can make hedgehog populations unviable.

In 2011 PTES, in partnership with the British Hedgehog Preservation Society (BHPS), launched a national campaign to conserve the hedgehog, a mammal that has declined in Britain by at least 25% since the year 2001.[10] The Hedgehog Street campaign has inspired thousands of people to make their gardens hedgehog-friendly and engage with their neighbours to make their entire streets accessible to hedgehogs, who desperately need our gardens to survive. [11]

As part of the joint campaign, PTES coordinates the European Hedgehog Research Group and convenes a steering group for the species, based on the previous BAP group, that includes the British Hedgehog Preservation Society, pre-eminent mammal ecologist Dr Pat Morris, and hedgehog enthusiast and author Hugh Warwick. In 2015 they produced the first conservation strategy for the species in the UK. The only UK training course on hedgehog-friendly land management, surveying and mitigation for professionals has also been developed and is being delivered around the UK.

In 2013 the campaign "Saving Big Cats and Wild Dogs" (shortened to "Saving Cats and Dogs") was launched. This is based around a website that provides information about the conservation projects that focus on wild felids and canids that are all supported through PTES grant funding. With a donation you can twin your pet cat or dog with a wild counterpart.[10]